Which of the following is NOT required for every farm tractor?

In Texas, the regulations for farm tractors specify certain lighting and reflector requirements for safety and visibility. Every farm tractor must be equipped with at least one tail light to ensure that it can be seen from behind, especially during low-light conditions. Similarly, the requirement for two head lamps ensures adequate illumination for the operator's forward visibility, which is crucial when operating on public roads or in dim conditions.

As for reflectors, the regulations state that tractors must have two red reflectors at the rear to enhance visibility to other drivers. However, the requirement for yellow reflectors is not mandated for all farm tractors. The purpose of yellow reflectors is often associated with certain types of slow-moving vehicles or specific equipment, rather than a blanket requirement for all farm tractors. Therefore, the lack of a requirement for two yellow reflectors makes this option the correct choice for what is NOT required.